1. Field of the Invention
The present invention relates to an adsorbent state determining apparatus for determining the state of an adsorbent arranged in an exhaust system of an internal combustion engine for adsorbing hydrocarbons in exhaust gases.
2. Description of the Prior Art
A conventional adsorbent state determining apparatus of the type mentioned above is known, for example, in Laid-open Japanese Patent Application No. 11-2115. This known determining apparatus is provided for determining a deterioration of an adsorbent. The determining apparatus is provided with temperature sensors at locations upstream and downstream of an adsorbent, respectively, for sensing internal temperatures at those locations, and compares times at which the two temperature sensors generate peak detected values when the adsorbent is in an adsorbing condition, or times at which time differentiated detected values of the two sensors reach peaks to determine the deterioration of the adsorbent. The determining approach as mentioned relies on the nature of the adsorbent. Specifically, the peak of the internal temperature of the adsorbent or the rising rate thereof occurs in the adsorbing condition, and the peak occurs earlier at an upstream location than at a downstream location. Also, as the adsorbent deteriorates, the peak occurs earlier at the downstream location. Thus, the determining approach can determine whether or not the adsorbent is deteriorated based on a comparison of the times at which the two temperature sensors present peaks, rather than temperature values detected thereby, without employing highly accurate temperature sensors.
However, the time at which the peak of the internal temperature or its rising rate of the adsorbent is reached during adsorption is not determined only by the state of the adsorbent, but varies in accordance with an operating state of an engine, just like the arrival time of exhaust gases which differs depending on the operating state of the engine, by way of example. In contrast, the prior art determining apparatus simply compares times at which the two temperature sensors present peaks of temperature values detected thereby or their time-differentiated values, irrespective of the operating condition of the engine, thereby failing to accurately determine the deterioration of the adsorbent.
In addition, since a temperature sensor has more or less a response delay, the response delay directly affects a time at which detected value reaches the peak, if the responsibility is low, possibly causing a further reduction in the accuracy of determining a deterioration. Furthermore, the adsorption performance of the adsorbent may be degraded by a variety of causes which include those resulting from attachment of soot, oil and the like on the adsorbent, and those resulting from a deterioration of the adsorbent itself. While the adsorption performance can be restored from the degradation resulting from the former causes, it cannot be restored from the degradation resulting from the latter causes. However, since the conventional determining apparatus senses the degraded adsorption performance based on the peak occurrence times irrespective of the cause, the adsorbent is likely to be determined as deteriorated even if its adsorption performance can be restored, in which case the opportunities for the adsorbent to demonstrate its performance are unduly narrowed so that the adsorbent fails to manifest its purifying action.
The present invention has been made to solve the problem mentioned above, and it is an object of the invention to provide an adsorbent state determining apparatus which is capable of accurately determining the state of an adsorbent including a deterioration as well as allowing for the recovery of the adsorbent if its adsorbent performance can be restored.
To achieve the above object, the present invention provides an adsorbent state determining apparatus for determining a state of an adsorbent arranged in an exhaust system of an internal combustion engine for adsorbing hydrocarbons within exhaust gases, characterized by comprising an upstream temperature sensor and a downstream temperature sensor positioned at locations upstream and downstream of the adsorbent in the exhaust system for detecting temperatures of exhaust gases upstream and downstream of the adsorbent, respectively; operating state detecting means for detecting an operating state of the internal combustion engine; downstream temperature estimating means for estimating the temperature of exhaust gases which should be detected at the location downstream of the adsorbent during adsorption of the adsorbent based on a detected upstream temperature detected by the upstream temperature sensor and the operating state of the internal combustion engine detected by the operating state detecting means; and adsorption state determining means for determining an adsorption state of the adsorbent by comparing the estimated downstream temperature estimated by the downstream temperature estimating means with the detected downstream temperature detected by the downstream temperature sensor during adsorption of the adsorbent.
According to this state determining apparatus, the temperatures of exhaust gases upstream and downstream of the adsorbent are detected by the upstream temperature sensor and the downstream temperature sensor, respectively. Also, the temperature of exhaust gases which should be detected downstream of the adsorbent during adsorption of the adsorbent is estimated based on the detected upstream temperature detected by the upstream temperature sensor, and the operating state of the internal combustion engine. Then, the adsorption state of the adsorbent is determined by comparing the estimated downstream temperature with the actually detected downstream temperature detected by the downstream temperature sensor during the adsorption of the adsorbent.
As the internal combustion engine is cold started, the heat of exhaust gases is absorbed by the cold adsorbent, when it passes therethrough, so that the downstream temperature during the adsorption rises with a delay in accordance with the adsorption performance of the adsorbent and a particular operating state of the internal combustion engine with respect to the upstream temperature. Also, as the adsorption performance of the adsorbent is degraded, the adsorbent can absorb a less amount of heat, causing the downstream temperature to rise earlier. It is therefore possible to appropriately determine an adsorption state of the adsorbent including the adsorption performance, while reflecting the operating state of the internal combustion engine, by calculating an estimated downstream temperature which should be detected on the downstream side when the adsorbent is normal in accordance with a detected upstream temperature and the operating state of the internal combustion engine, and comparing the estimated downstream temperature with the actually detected downstream temperature during the adsorption.
Preferably, the adsorption state determining apparatus further comprises response delay compensating means for compensating at least one of the upstream temperature sensor and the downstream temperature sensor for a response delay.
According to this preferred embodiment, the response delay compensating means compensates the upstream temperature sensor and/or the downstream temperature sensor for a response delay, thereby making it possible to maintain the accuracy for determining the adsorption state of the adsorbent even if actually used temperature sensors have a low responsibility.
Preferably, in the adsorption state determining apparatus, the adsorbent is configured to desorb hydrocarbons once adsorbed thereby, wherein the adsorption state determining apparatus further comprises desorption state determining means for determining a desorption state of the adsorbent; and desorption state storing means for storing the desorption state of the adsorbent determined by the desorption state determining means, wherein the adsorption state determining means determines adsorption performance of the adsorbent in accordance with the desorption state stored in the desorption state storing means in a preceding operation of the internal combustion engine.
According to this preferred embodiment, the desorption state determining means can determine a desorption state of the adsorbent. The adsorption state determining means in turn determines the adsorption performance of the adsorbent in accordance with the desorption state in the preceding operation of the engine. It is therefore possible to avoid determining the adsorption performance of the adsorbent with hydrocarbons and the like remaining on the adsorbent, for example, because of uncompleted desorption in the preceding operation, and erroneous determination on the adsorption performance which would be otherwise made in such a situation.
Preferably, in the adsorbent state determining apparatus, the exhaust system includes a main passage, a bypass passage circumventing the main passage and having the adsorbent arranged therein, and switching means for switching an exhaust passage to the main passage and to the bypass passage, wherein the exhaust passage is switched to the bypass passage by the switching means at a start of the internal combustion engine to adsorb hydrocarbons within exhaust gases on the adsorbent, and subsequently the exhaust passage is switched to the main passage by the switching means to desorb the hydrocarbons adsorbed on the adsorbent by exhaust gases.
According to this preferred embodiment, after the internal combustion engine is started, the exhaust passage is switched to the bypass passage to adsorb hydrocarbons contained in exhaust gases on the adsorbent. Then, with the exhaust passage switched to the main passage, adsorbed hydrocarbons are desorbed from the adsorbent by exhaust gases. This preferred embodiment also provides the advantageous effect described above.
Preferably, the adsorbent state determining apparatus further comprises exhaust gas flow rate parameter detecting means for detecting a parameter representative of a flow rate of exhaust gases, wherein the desorption state determining means determines termination of desorption of hydrocarbons from the adsorbent in accordance with the exhaust gas flow rate parameter detected by the exhaust gas flow rate parameter detecting means during desorption of the adsorbent.
According to this preferred embodiment, the completion of desorption of hydrocarbons from the adsorbent is determined in accordance with the exhaust gas flow rate parameter detected during the desorption. Since the desorption of the adsorbent is performed by exhaust gases, the degree of desorption and the flow rate of exhaust gas during the desorption are in a mutually close relationship, and have a high correlation to each other. It is therefore possible to simply and appropriately determine the completed desorption of the adsorbent in accordance with the exhaust gas flow rate parameter during the desorption.
Preferably, the adsorbent state determining apparatus further comprises recovery control means for conducting a recovery control for restoring the adsorption performance of the adsorbent when the adsorption state determining means determines that the adsorption performance of the adsorbent has been degraded and when the desorption state determining means determines that the adsorbent has completed desorption.
According to this preferred embodiment, the recovery control is conducted for restoring the adsorption performance of the adsorbent when it is determined that the adsorption performance of the adsorbent has been degraded, so that the adsorbent can be recovered by the recovery control when the degraded adsorption performance is caused by attachment of sooth, oil and the like on the adsorbent and hence can be restored. Also, since the recovery control is conducted only when the adsorbent has completed the desorption, it can be ensured to avoid the emission of adsorbed hydrocarbons to the atmosphere by the recovery control before desorption or during desorption.
Preferably, in the adsorbent state determining apparatus, the adsorption state determining means again determines the adsorption performance of the adsorbent after the recovery control has been conducted to determine a deterioration of the adsorbent in accordance with the result of determination.
According to this preferred embodiment, the adsorption performance of the adsorbent is again determined after the recovery control has been conducted to determine a deterioration of the adsorbent in accordance with the result of determination. Thus, a deteriorated adsorbent is determined as definite only when the adsorption performance cannot be restored by the recovery control, thereby making it possible to appropriately determine a deteriorated adsorbent in accordance with the cause by which the adsorption performance is degraded.